SBR systems are used to treat wastewater. A typical conventional SBR system includes one or more SBRs which contain a large population of microorganisms that ingest contaminants in the influent wastewater to form biological flocs and treat the wastewater. SBR systems typically use four phases to treat wastewater: fill, react, settle, and decant. During the fill phase, the SBR is filled with the influent wastewater and may be aerated, mixed without aeration, or not mixed and not aerated. The react phase involves adding oxygen, mixing, or a combination thereof, to provide treatment by converting biochemical oxygen demand (BOD) to microorganisms to form biological flocs. During the settle phase, the biological flocs formed in the previous phases are allowed settle to the bottom of the SBR to form settled sludge. The decant phase involves slowly decanting the clear water from the settled sludge to provide a treated effluent.
However, during the settling phase of a typical conventional SBR system, the biological flocs are only marginally heavier than water and therefore settle very slowly. Moreover, the solids separation in the settle phase may be unreliable due to many types of settling problems that are caused by: overgrowth of filamentous organisms, viscous bulking caused by the overgrowth of either zoogleal organisms or exocellular polysaccharide material, pin floc, straggler floc, and the like. This may limit the capacity of a conventional SBR system and can compromise the quality of the treated effluent.